224 research outputs found
Charge manipulation and imaging of the Mn acceptor state in GaAs by Cross-sectional Scanning Tunneling Microscopy
An individual Mn acceptor in GaAs is mapped by Cross-sectional Scanning
Tunneling Microscopy (X-STM) at room temperature and a strongly anisotropic
shape of the acceptor state is observed. An acceptor state manifests itself as
a cross-like feature which we attribute to a valence hole weakly bound to the
Mn ion forming the (Mn) complex. We propose that the observed
anisotropy of the Mn acceptor wave-function is due to the d-wave present in the
acceptor ground state.Comment: Proceedings of the SIMD-4 conference. Hawaii, USA (December 1-5,
2003
Photoemission studies of GaMnAs: Mn-concentration dependent properties
Using angle-resolved photoemission, we have investigated the development of
the electronic structure and the Fermi level pinnning in GaMnAs
with Mn concentrations in the range 1--6%. We find that the Mn-induced changes
in the valence-band spectra depend strongly on the Mn concentration, suggesting
that the interaction between the Mn ions is more complex than assumed in
earlier studies. The relative position of the Fermi level is also found to be
concentration-dependent. In particular we find that for concentrations around
3.5--5% it is located very close to the valence-band maximum, which is in the
range where metallic conductivity has been reported in earlier studies. For
concentration outside this range, larger as well as smaller, the Fermi level is
found to be pinned at about 0.15 eV higher energy.Comment: REVTeX style; 7 pages, 3 figure
Bloch surface waves-controlled fluorescence emission: coupling into nanometer-sized polymeric waveguides
The lateral confinement of Bloch surface waves on a patterned multilayer is investigated by means of leakage radiation microscopy (LRM). Arrays of nanometric polymeric waveguides are fabricated on a proper silicon-nitride/silicon-oxide multilayer grown on a standard glass coverslip. By exploiting the functional properties of the polymer, fluorescent proteins are grafted onto the waveguides. A fluorescence LRM analysis of both the direct and the Fourier image plane reveals that a substantial amount of emitted radiation couples into a guided mode and then propagates into the nanometric waveguide. The observations of the mode are supported by numerical simulations
Nano-probing station incorporating MEMS probes for 1D device RF on-wafer characterization
International audienc
Band offsets at zincblende-wurtzite GaAs nanowire sidewall surfaces
The band structure and the Fermi level pinning at clean and well-ordered sidewall surfaces of zincblende (ZB)-wurtzite (WZ) GaAs nanowires are investigated by scanning tunneling spectroscopy and density functional theory calculations. The WZ-ZB phase transition in GaAs nanowires introduces p-i junctions at the sidewall surfaces. This is caused by the presence of numerous steps, which induce a Fermi level pinning at different energies on the non-polar WZ and ZB sidewall facets.This study was financially supported by the
EQUIPEX program Excelsior, the European Community’s
Seventh Framework Program (Grant No. PITN-GA-2012-
316751, “Nanoembrace” Project) and the Impuls- und
Vernetzungsfonds of the Helmholtz-Gemeinschaft Deutscher
Forschungszentren under Grant No. HIRG-0014. T. Xu
acknowledges the support from the National Natural Science
Foundation of China (Grant No. 61204014)
Spin Waves in Disordered III-V Diluted Magnetic Semiconductors
We propose a new scheme for numerically computing collective-mode spectra for
large-size systems, using a reformulation of the Random Phase Approximation. In
this study, we apply this method to investigate the spectrum and nature of the
spin-waves of a (III,Mn)V Diluted Magnetic Semiconductor. We use an impurity
band picture to describe the interaction of the charge carriers with the local
Mn spins. The spin-wave spectrum is shown to depend sensitively on the
positional disorder of the Mn atoms inside the host semiconductor. Both
localized and extended spin-wave modes are found. Unusual spin and charge
transport is implied.Comment: 14 pages, including 11 figure
Monte Carlo simulations of an impurity band model for III-V diluted magnetic semiconductors
We report the results of a Monte Carlo study of a model of (III,Mn)V diluted
magnetic semiconductors which uses an impurity band description of carriers
coupled to localized Mn spins and is applicable for carrier densities below and
around the metal-insulator transition. In agreement with mean field studies, we
find a transition to a ferromagnetic phase at low temperatures. We compare our
results for the magnetic properties with the mean field approximation, as well
as with experiments, and find favorable qualitative agreement with the latter.
The local Mn magnetization below the Curie temperature is found to be spatially
inhomogeneous, and strongly correlated with the local carrier charge density at
the Mn sites. The model contains fermions and classical spins and hence we
introduce a perturbative Monte Carlo scheme to increase the speed of our
simulations.Comment: 17 pages, 24 figures, 2 table
Efficient photogeneration of charge carriers in silicon nanowires with a radial doping gradient
From electrodeless time-resolved microwave conductivity measurements, the
efficiency of charge carrier generation, their mobility, and decay kinetics on
photo-excitation were studied in arrays of Si nanowires grown by the
vapor-liquid-solid mechanism. A large enhancement in the magnitude of the
photoconductance and charge carrier lifetime are found depending on the
incorporation of impurities during the growth. They are explained by the
internal electric field that builds up, due to a higher doped sidewalls, as
revealed by detailed analysis of the nanowire morphology and chemical
composition
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